The invention relates to a method for etching at least one ion track so as to form a pore in a membrane and an electrolyte cell for preparing such a membrane from a foil for use as a separation membrane or as a membrane in a measuring or control system or in a sensor.
Membrane technology is a rapidly growing field with applications of large economical and ecological consequences and importance. Homogenous, responsive membrane systems which can control the flow of substances are quite advanced and are already widely utilized. Heterogeneous composite membranes, which are based on hydro-gels and are manufactured mechanically on strong substrates, are already known in the art.
An electrolytic cell with two electrolytes to be separated by a membrane can be operated as an electrically controlled valve. It can further be stimulated in its behavior thermically and/or by the pH value and/or the pH value gradient and/or by chemical compounds to be detected in the electrolytes (sensor function). It can also be used for transferring certain substances from one cell half through the membrane to the other cell half in a controlled manner. (actor function, chemical valve). With its pore area the membrane separates in the electrolyte cell a first electrolyte, the “inner phase”—in medication dosing apparatus this is the medication reservoir—from the second electrolyte, the “outer phase”—in medication dosing apparatus, this is the body liquid—without any further action.
If the membrane in its matrix consists of an organic polymer then the absorption of water is based on the presence of polar groups in the network of the polymer. The degree of swelling depends on the temperature, the pH value and the concentration of dissolved substances. So-called hydro-gels can swell by more than 100%. Their swelling properties can be imprinted for a specific stimulation by an addition or copolymerization of specific chemical groups. The switching time of these so-called thermo-responsive membranes is in a minute range.
The permeation of dissolved substances increases with the degree of swelling of the membrane and is determined by pressure gradients and the concentration. For swelling, water must enter the polymer matrix. The time required for the water to enter increases exponentially with the thickness of the hydrogel. The volume flows of the substances to be transported rapidly decrease with increasing thickness of the hydro-gel. It is therefore important that the membrane to be penetrated is as thin as possible. The physico-chemical stopping is one known technique to manufacture ultra-filtration and reverse osmosis membranes with a very thin active layer of a few nm thickness. These filters are already widely used in connection with rigid-pore filters with ultra-fine pores. The stimulus-responsive ion-track membrane permits the manufacture of a hydro-gel layer with a thickness of several micrometers. The switching is therefore quite slow, that is, it has a time constant in the area of minutes. The thermo-responsive chemical valve provides for an electrical switching of the permeability by the application of an electrical current selectively, that is, only the pores, not the whole membrane are heated and the switching can therefore be controlled rapidly. However, the active layer of the membrane is in the thickness range of the membrane (1 to 100 micrometer).
The main problems of the state of the art are that the membranes described have too long a response time or too low a permeability corresponding to the thickness of the active layer.
It is therefore the object of the present invention to provide a membrane system which provides for an extremely fast release of chemical substances that is within milliseconds to fractions of a second, has an inherent sensor capability, and provides for an electric control of the transferred substance.